The fine structure of lymphoid tissue from patients with primary or secondary immune deficiency diseases will be studied. Information from that study will be correlated with clinical and immunological data from the same patients. The information will also be compared with similar data from human lymphoid tissue from individuals with normal immune competence. Parallel studies using animal models will concentrate on correlated fine structural and immunological techniques directed toward an understanding of the normal differentiation of the B-lymphocyte and T-lymphocyte systems, their mechanism of normal function, and the steps of differentiation and function where blocks may occur to result in immune deficits. The tissue to be studied will include lymphoid tissue from chickens, mice and rabbits. Thymus from Snell-Bagg pituitary dwarf mice will be compared with normal mice. Stem cells from embryonic chicken yolk sac, bursa, and thymus will be studied ultrastructurally. The effect of sex and adrenal steroid hormones on mouse thymus, spleen and peripheral blood lymphocytes will be determined. The effect of pokeweed mitogen and antigenic stimulation on B-lymphocytes in chicken bursa and rabbit appendix will be studied. The role of lysosomes in the handling of antigens by follicle-associated epithelium will be determined.